Detector



Aug. 11,1936g A J. w. coNKLlN DETECTOR Filed Jan. 28, 1935 oNKLlN WCA.

I INVENTOR- JAMES W.

TTORNEY- mug Patented Aug. 11, 1936 UNITED STATES PATENT" @FFME DETECTOR James .W. Conklin, Rocky Point, N.V Y., assignor to Radio Corporation of America, a corporation of Delaware Application January 28, 1933,. Serial No. 653,946

8 Claims.

modulating waves, the phase of which varies in accordance with the signal.

The ordinary radio receiver is insensitive to phase modulation. I-Ieretofore elaborate and complicated methods and means have been employed to receive and demodulate phase modulated waves.

The primary object of the present invention is to provide a new and improved method of and means for demodulating phase modulated waves, which method and means is simple in nature and eiiicient in operation.

In the method which I prefer, I use an oscillating detector of the autodyne type. The signal is passed through a radio frequency amplifier, the purpo-se of which is to raise the energy level of VVthe signal to a suitable value and to maintain it there by a limiting action. This limiting action may be obtained in any manner. Preferably, it is obtained by passing the modulated .wave through radio frequency amplifiers operating at saturation. The limited signal is then impressed on the autodyne detector circuit through a coupling coil and the degree of coupling carefully adjusted to give a signal level which is just sufficient to hold the oscillating detector in stepwith the incoming carrier when the detector has been adjusted to Zero beat note. Iriasmuch as the carrier is the most predominating frequency with ordinary modulation levels,

35 attainment of this adjustment is not at all .The action of the detector under these circumstances is to supply a strong local carrier essentially locked in phase with the incoming carrier.. In a sense, the oscillating circuit tuned to` zero beat provides a very sharp filter and amplifier for the carrier frequency alone. When the incoming signal varies in phase with modulation, the effect is to vary the efficiency of the Ituned circuit as far as the detector tube is concerned, i. e., when the incoming signal leads in phase, it will supply energy to the circuit and when it lags in phase it will eiectively load the circuit.

This action may be best understood by analogy.

' Consider the-tuned circuit to be an alternator with; the detector tube as the driving motor. The incoming signal is an outside source connected tothe alternator; When the signal voltage has Vthe samephase asl the alternator, there will be (Cl. Z50-20) no transfer of -energy and the motor will be supplying the losses in the alternator. If the signal voltage advances-in phase, it will tend to drive the alternator as a'motor and relieve the load on the motor,and vice versa. Just as the driving motor current will react to these phase shifts, so will the detector plate current.

This circuit is sensitive and efficient for phase modulation reception. The receiver involves little more equipment than a simple receiver, such as used for telegraph reception. As itA involves no fixed filters, it may be used on any frequency directlyand can be built much more cheaply and compactly than other types of phase modulation receivers.

The novel features of my invention have been pointed out with particularity in the claims appended hereto. My method of demodulating waves and a practical circuit for carrying out the same will be best understood from the following description thereof and therefrom when read in connection with Vthe attached drawing, in which:

Figures l and 2 illustrate my phase demodulation circuit including the autodyne demodulating means.

In practice, my receiver would have the following components:

l. Means for intercepting kthe waves. This means may bean aerial system l of any appropriate type.

2. Means vfor amplifying the radio frequency signal to a'suitable level. Amplifying in any manner the intercepted Wave.

3. Means for limiting or controlling the maximumr output of the amplifier. Any amplitude limiting device may be used. I propose to use a saturated radio frequency amplifier.V

4.1Means for coupling the output of the ampli-fierto the detector and means for controlling the value of that' coupling.

5. An autodyne type of detector with means for controlling the tuning and strengthv of oscillations.

6. Suitable audio amplifiers and output circuits;

The .aerial l iscoupl'ed by inductance 8 to the 'grid type.

biased to the desired operating potential by current from a source I3. The tube I2 may be of any type and is shown as a tube of the screen grid type. The anode of tube I2 is connected to a tuned circuit I4 including inductance and capacity in parallel.

While I have shown a single amplifier in the radio frequency amplifying stage, it will be understood that several amplifiers may be used if necessary to raise the signal to the desired level. The high frequency oscillations selectively amplified in the tube I2 are impressed from the oscillation circuit I4 by way of .a coupling capacity I6 on to the control grid of a thermionic tube I8 in the limiting amplier stage. The tube I8 has its control grid biased by way of resistance I'I and source 20 to operate at saturation so that the oscillations appearing in the output inductance 2i, connected with the anodeof tube I8, will be of constant amplitude. Here I have shown but a single tube in the limiting amplifier. If necessary several tubes may be used. Furthermore, the tubes may be of any type, although I have shown the tube I 8 as being of the screen The screen grid electrodes of tubes IB and I2 may be supplied with the desired potential by a lead 2| connected with the potential source 22.

The autodyne detector includes a thermionic tube 24 having its input electrodes connected with an input circuit comprising an inductance 25 and a capacity 3| in parallel and its output electrodes connected to a Work circuit including 35 lthe primary winding 25 of a transformer T. The

anode circuit of 24 is inductively coupled to the input circuit by Way of an inductance 2'I and capacitively coupled to the input circuit by the capacity 28 in series with the inductance 2'I. Best results are obtained from this receiver if a sensitive control of regeneration in the autodyne detector is provided. For this reason regeneration is obtained by variable inductive and capacitive coupling between the output electrodes of the tube 24 and the input electrodes of the .tubel 24. When the signal is varying in intensity the limiter, including the amplifier I8, is an essential feature. As is well understood by those skilled in the art, the limiter serves to level off the amplitude of the signals as passed through the amplifier I8. This is to insure that the signal energy impressed on the input circuit 25 of the autodyne detector is just sufficient to hold this detector in step with the incoming signal. If more signal is impressed on the detector circuit than is necessary to just hol-d the detector in step, the detector will be pulled in phase Ywith the incoming signal and the signal modulation will disappear from the output circuit of the detector. To further insure that the proper amount of signal energy is impressed from the final limiter tube I8 on to the autodyne detector 24, the inductance 2l in the output circuit of the tube I 8 is variably `coupled to the inductance in the input circuit 25 of the autodyne detector. An electrostatic shield, similar to the one between windings 8 and I0, may be interposed between 2| and 25.

Radio frequency oscillations are blocked out of -the transformer T by a radio frequency choking inductance 34. As the incoming signal varies in phase with modulation the efficiency of the tuned circuit 25v is varied. VWhen the incoming signal leads in phase the efficiency ofthe tuned circuit,

as far as the detector circuit is concerned, Will decrease and the incoming signal will supply energy to the circuit. When the phase of the incoming signal lags the phase of the oscillations in the tuned circuit it will act in effect as a load on said circuit. This will c-ause the amplitude 5 of the rectified currents in the output circuit of the autodyne 24 to vary in accordance with the signal modulation. These variations will be impressed by the transformer T on to the audio frequency amplifier tube 30, from which it may be 10 impressed by a transformer Ti on to any indicator. The tuning capacity 3l in the tuned circuit 25 may be shifted by a trimmer condenser 32 in order that a single control may be used for this tuning capacity and the tuning capaci- 15 ties in the prior stages.

Anode potentials for the tubes I2, I8, 24 and 3U may be supplied from separate sources or from the single source 22, as shown.

Although I have shown an autodyne detector 20 operated in a novel manner to demodulatephase modulated waves, it will be understood that this method may be applied to a. superheterodyne of the ordinary type, that is, the superheterodyne which includes a source of local oscillations. 25 l" When this is done the limiting action and detecting in part of the amplification may be accomplished in the intermediate frequency amplifier. The second detector of the heterodyne, however, will be replaced by my novel autodyne 30 detector including the adjustable coupling circuits and regeneration controls.

The method of and circuit for demodulating phase modulated waves as disclosed above has been used in practice by me and has proved to be efficient and successful in operation.

Having thus described my invention and the operation thereof, what I claim is:

1. A signal demodulating circuit comprising, an energy absorption member, a radio frequency amplifier having its input electrodes coupled to said absorption member, a second radio fre-l quency amplifier having its input circuits coupled tothe output circuits of said rst named radio frequency amplifier, means for biasing the electrodes of said second named radio frequency amplier to a potential at which it operates at satp uration, an autodyne detector including a thermionic tube having variably coupled input and output electrodes, and a variable coupling cir- Cuit for loosely coupling said autodyne detector to the output electrodes of said last named radio frequency amplifier.

2. A signal demodulating circuit comprising, an' energy absorption member, a radio frequency amplifier having its input electrodes coupled to said absorption member, a second radio frequency amplifier having its input electrodes capacitively coupled to the output electrodes of said first named radio frequency amplifier, a circuit in- 6011 cluding a direct current sourceV for biasing the electrodes of said second named radio frequency amplifier to a potential at which it operates atk saturation, an autodyne detector including a thermionic tube having inductive and capacitive coupled input and output electrodes, and an inductive circuit for loosely coupling said autodyne Y tothe output electrodes of said last named radio frequency amplifier.

3. Means for demodulating signal carrying os- -z to said signal responsive circuit and an output circuit, means in one of said circuits to insure substantially constant amplitude of the signal modulated oscillations in said output circuit irrespective of amplitude variations in the signal modulated oscillations in said input circuit, demodulating means of the thermionic type having input and output circuits coupled to produce oscillations, and means for loosely coupling the input circuit of said demodulating means of the thermionic type to the output circuit of said radio frequency amplifier.

4. Means for demodulatng signal modulate oscillations of constant amplitude comprising, a radio frequency a-mplier operating at saturation, said amplier having an input circuit to which said oscillations to be demodulated are applied and an output circuit, a second thermionic tube having input and output electrodes, an input circuit coupled between said input electrodes, said circuit including an inductance loosely coupled to an inductance in the output circuit of said first named tube, an output circuit connected between the output electrodes of said second named tube, and means including an inductance and a variable capacity for coupling said output circuit of said second named tube to the input circuit of said second named tube to insure the production of oscillations in said second named tube and circuits of constant amplitude.

5. A phase modulated wave demodulating device comprising, a thermionic tube having an anode, a cathode and a control grid electrode, a tuned inductance connected in series with an impedance between the control grid and cathode of said tube, an output circuit connected between the anode and cathode of said tube, said output circuit being coupled to indicating means, an inductance and a variable capacity connected between the anode of said tube and the cathode of said tube, said inductance being coupled to said first mentioned inductance, and variable loose coupling Ameans for applying signal modulated oscillations of substantially constant amplitude to said first mentioned inductance.

6. Means for demodulating oscillations of constent amplitude but of a phase which varies at signal frequency comprising, a thermionic amplifier having input electrodes connected in an input circuit including biasing means and an inductance adapted to be energized by said oscillations to be demodulated and output electrodes, the biasing means in said input circuit insuring operation of said amplier at saturation whereby the amplitude of the oscillations on said output electrodes is constant irrespective of change in amplitude of the oscillations impressed on said inductance in said inputcircuit, the phase of said oscillations varying at signal frequency, a second thermionic tube having its input and output electrodes connected in circuits variably coupled to produce oscillations and tuned to a frequency which is the mean of the frequency of the oscillations to be demodulated, and inductive means coupled with the output electrodes of said first named tube and loosely coupled to the input circuit of said second named tube for applying the oscillations of constant amplitude and varying phase from the output electrodes of said iirst named tube to the input electrodes of said second named tube.

'7. In a system having a stage of autodyne detection followed by at least one stage of amplification and useful for olemodulation of phasemodulated signals, the method of detection of said signals which comprises loosely coupling said stage of autodyne detection with said stage of ampliiication, operating the amplication stage under a condition of such saturation as to substantially level off the amplitude of the received signals so that the signal level is just suiiicient to hold the locally generated oscillations in step with the incoming carrier, and adjusting the frequency of the locally generated oscillations so as to maintain a Zero beat note with said carrier.

8. In a system for demodulation of phasemodulated signals, the method of detection of said signals which comprises collecting, amplifying and leveling off the amplitude of an incoming phase-modulated radio-frequency wave, locally generating a strong carrier wave, loosely coupling the incoming wave to said locally generated wave,

causing the locally generated wave to be adjusted in frequency and in phase so as to have a zero beat with the carrier component of said incoming wave, causing said locally generated wave and said incoming carrier wave component to be locked in step, and causing the strength of the locally generated wave to be varied in accordance with variations in the percentage of phase-modulation.

JAMES W. CONKLIN. 

